Signaling system



Oct. 12, 1948. c). A. SHANN 2,450,997

smmmme SYSTEM Filed llay 23, 1945 2 Sheets-Sheet 2 INVENTOR Q A. SHAN/VA TTORNE Y Patented Oct. 12, 1948 UNITED STATES PATENT OFFICE- SIGNALINGSYSTEM Oscar A. Shann, Short Hills, N. J., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication May 23, 1945, Serial No. 595,302

3 Claims. 1

This invention relates to communication systems and particularly tostation arrangement to permit emergency operation.

The object of the invention is to provide a special device by which asubscriber may dispense with the requirement to deposit a coin in orderto make a call. The said special device may be in the form of areclaimable token in the possession of a particular subscriber which hascertain peculiar properties by virtue of which the substation circuit ofa coin box station may be operated.

In accordance with the present invention a token is provided having onthe surfaces thereof a number of electrical contact surfaces and withinthe body thereof a. plurality of changeable electrical circuits betweensuch surfaces. The token, described in another manner, may consist of adisc of thermistor material provided with a plurality of electrodeswhereby a plurality of electrical paths through said material areprovided, which paths due to the nature of the material are changeablyresponsive in their resistances to the current flowing therethrough.

The invention comprises the use of such a token in a responsive circuitwhereby a new and desirable result may be obtained.

The combination of this new token and the responsive circuit may beused, by way of example, to make emergency calls over coin box telephonestations. session of an authorized person and may be reclaimable, thatis, it may be arranged for temporary use in the coin box apparatus andnot subject to deposit in the manner of an ordinary COlll.

A feature of the invention is a token shaped like an ordinary coinhaving changeable electrical circuits therein between different pointson its surface.

Another feature of the invention is the combination of a token havingchangeable electrical circuits between different points on its surfaceand a circuit responsive to the insertion of said token therein forproducing a result differing from the insertion of any other materialeither conducting or insulating therein.

Another feature of the invention is the arrangement in substationapparatus for operating a calling circuit either by the deposit of acoin or the reclaimable insertion in the coin slot of a special token.

In accordance with another feature the special token by virtue of itsinternal resistance may be The token may be in the pos- 2 made toproduce a, vibration whose frequency depends on the value of saidinternal resistance. In accordance with this feature different tokensmay thus be provided to produce difierent tones which maybe used asidentification signals.

Another feature of the invention is a circuit arrangement for operatinga. coin box telephone circuit responsive to the change in resistance ofa special token inserted therein and unresponsive to any other conditionestablished by the use of a token of unchangeable resistance.

Other features will appear hereinafter.

The drawings consist of eight figures as follows:

Fig. 1 is a plan view of the special token;

Fig. 2 is a cross-sectional view of the same;

Fig. 3 is a schematic circuit diagram showing the equivalent resistancepaths within the token;

Fig. 4 is a circuit diagram with a schematic representation of themechanical arrangement of the slider apparatus in which the specialtoken may be used;

Fig. 5 is an equivalent circuit diagram of the arrangement shown in Fig.4 where the special token is in circuit;

Fig. 6 is a similar equivalent circuit diagram showing the connectionswhich would be established were a. coin or metal slug put in the slider;

Fig. 7 is a figure like Fig. 4 showing an alternative arrangement inwhich the changing resistance of the special token is used to cause theproper response; and

Fig. 8 is a fragmentary drawing showing a safety device which might beused.

This invention is embodied in the construction and the use of aspecially constructed token, the size of the usual coin used in the coinslot of a telephone substation instrument. The token is shown in Figs. 1and 2, where Fig. l is a plan view showing a conducting ring I and aconducting disc 2 embedded in and flush with the remainder of thesurface 3. The conducting parts may be of brass, copper, silver or anyother appropriate metal of comparatively low electrical resistance. InFig. 2 where the token is shown in cross-section it is seen that asimilar ring 4 and d sc 5 is embedded in the opposite surface and thatthe interior of the token is filled with a thermistor compound, amaterial having the property of presenting a high resistance electricalpath therethrough when cold and a low resistance path whenheated, as bythe flow of current therethrough.

The dimensions of the token 'are such that the resistances between thevarious conducting rings and discs may be shown in'Fig. 3. Theresistance between the ring I and disc 2 is comparatively low, betweenring 4 and disc 5 is comparatively low and the other paths, such as thatbetween rings I and 4 or between discs 2 and I, are comparatively high.When ,the token is placed in circuit, the current fiow will cause thecomparatively low resistance paths to heat and thus become very muchlower while the comparatively high resistance paths will remainsubstantially unafl'ected.

Fig. 4 shows an arrangement in which the token above described may beusefully employed for the special purpose of making a. call over atelephone line from a substation which ordinarily requires the depositof a coin. The apparatus here shown is in addition to the conventionalapparatus present at such a station.

The arrangements include a slider type coin slot here used only inconnection with the special token above described. The slider 'I may bepulled out until a recess in such slider is outside the wall 8 of thedevice so that the special token 9 may be inserted therein. The slideris then pushed back into the position shown so that the fingers I0, I I,I2 and I3 come into contact with the contact surfaces of the token.

Two detecting relays I4 and I5 are employed of which I4 is marginal sothat it will fail to respond to anything less than a direct connectionbetween the fingers I and I3. When the special token is first insertedin the slot, the connections shown in Fig. 4 will be established and thetwo relays I4 and I will be included in a circuit the equivalent ofwhich is shown in Fig. 5. A circuit may be traced from the battery I5,through the winding of the marginal relay l4, contact finger I3, thethermistor material of the token to finger I2, the connection to fingerII, the thermistor material of the token to the contact finger III, thewinding of sensitive relay I 5 to the battery I5. At first theresistance of the thermistor material is so high that neither of theserelays respond, but as the current flows through the circuit described,such resistance changes and in a short time the condition pictured inFig. 5 is established. Here the resistance between the fingers I3 and I2is shown as a low resistance I1, the resistance between the fingers IIand I 0 is shown as a low resistance I8 and the resistance between thefingers I3 and I0 is shown as a high resistance l9 which does not changeto any appreciable degree. As these resistances I1 and I8 become low thecurrent in the circuit described increases until relay I5 operates butthe marginal relay I4 does not respond. Therefore a circuit for relay isclosed from battery 2|, armature and back contact of relay I4, windingof relay 20, armature and front contact of relay I5 to battery 2 I.Relay 20 responds and grounds the tip of the telephone line 22, thuscalling in the operator or otherwise rendering the line active inconventional manner.

As an alternative or additional means, the primary 23 of an inductioncoil or transformer 24 may be connected to the fingers I0 and II and aback contact for the armature of relay I5 may be provided. In this casethe winding of the relay I5 is to designed that it will respond to thelow resistance I1 but will not respond to the resistances I1 and I8 whenin series. Therefore as the resistances I1 and i8. reach their lowvalues, the armature I5 will vibrate and thus produce a tone in the coil24 which may be transmitted over a telephone line 25 to notify anoperator that a call is being made by one specially privileged to do soby possession of such a special token.

Should an unauthorized person attempt to use this special service byinserting a coin or a metal disc in the slot of the slider, the circuitcondition shown in Fig. 6 will be established. Here the relays I4 and I5are included in a direct connection, and the marginal relay as well asthe sensitive relay I5 will respond so that the circuit for relay 2!!closed by relay I5 is opened at another point by relay I4 with theresult that relay 2! fails to operate. Thus an unauthorized personcannot make a call by inserting a coin in the slider I from which it maybe recovered but must perforce make the call in the conventional mannerby inserting the coin in the regular apparatus from which it cannot berecovered except of course by an action of the operator.

In Fig. 7 an alternative arrangement is shown in which two tests aresequentially made to determine first that the token inserted is of highresistance and second that it has later changed its resistance to alower value whereby the changing characteristic of this token isrecognized. In Fig. 7, the slider 25 is shown by the connection at itsright-hand end to be grounded (being of metal and being electrically incontact with the frame of the apparatus). Here the slider is onlypartially pushed home to illustrate the action which takes place duringthe operation. At this stage a connection will be established from agrounded battery, through marginal relay 25 which will respond tonothing less than a direct connection to ground, through contacts 21which may be operated by the conventional switchhook, the finger 28, thering 29 of the token 30, the thermistor material therein, the ring 3I,the finger 32 and the marginal relay 33 to ground. Neither the relay 25nor the relay 33 will respond in this circuit if the resistance of thethermistor material between the'rings 29 and 3| is high, as it should beat this stage of the operation, nor will either of these relays respondwhen the slider has been pushed all the way home until fingers 34 and 35come in contact with the rings 23 and II respectively and the fingers 28and 32 come in contact with the discs 35 and 31 respectively, in thesomewhat lower resistance circuit provided by the token (as indicated inFig. 3), until the thermistor material has become heated. At this stage,however, a relay 38 has been placed in series and which will respond assoon as the thermistor material lowers its resistance through heating.The circuit for relay 38 may be traced from grounded battery relay 25,contacts 21, finger 28, disc 35 and comparatively lower resistancebetween disc 35 and ring 23, finger 34, winding of relay 38, finger 35,ring 3I, the comparatively lower resistance between ring 3| and disc 31,finger 32, winding of relay 33 to ground. With the slider in its homeposition the added resistance of the relay- 35 in series with thewinding of relay 33 will prevent the operation of relay 33 even when thethermistor material changes to a low resistance value. Relay 35, whichis the most sensitive of the three relays, will not respond at first,but as the thermistor material becomes heated, will at length operateand through its armature I will short-circuit the marginal relay 33 toprevent its operation. Relay 33 also closes a circuit from ground, itsarmature 2 and front contact the back contact and armature of relay 25,the tip of the telephone line 39 to signal the central ofllce. It shouldbe noted that even after the finger 32 is directly grounded by theoperation of relay 38 the resistance of relay 38 will prevent thatdirect connection needed by the marginal relay 26 for its operation.

If a. coin or metal slug is placed in the slot, then through its contactwith theslider material it will provide a direct path to ground forrelay 26 and cause this relay to operate so that the connection to thetip of the line 39 cannot be completed. At the same time both relays 33and 38 will be short-circuited and cannot operate.

If a plastic or other non-conducting token is placed in the slot, thennone of the relays will operate.

If some ingenious person should attempt to place in the device acoin-shaped piece of material, such as a carbon disc, which might havethe heated resistance characteristic of the special token, then therelay 33 would operate as the slider comes into the position shown inFig. '7. In, this case relay 33 would not have the resistance of relay38 in series with it and would respond to the circuit established with acomparatively low resistance between fingers 28 and 32. Relay 33 inresponding will short-circuit relay 38 and thus prevent its operation.Relay 33 is shown as slow releasing, though it is not necessary to makethis relay able to hold over any more than a very few milliseconds asthe time taken for a person to push the slider from the position shownin Fig. 7 to its final position will never be long or more than the saidfew milliseconds. Therefore the relay 33 tends to lock itself inoperated position for by short-clrcuiting the relay 38 it assures itselfof sumcient operating current to maintain itself in operation. Thus anattempt to simulate the action of a, special token with an unchangeableresistance disc will be defeated.

Fig. 8 shows an additional device which may be introduced for safetypurposes though it will be understood that such safety devices willordinarlly be included when practical considerations call for them. Inthis case an arm 40 is normally stressed toward the left by a spring 4|against a stop pin 42. When a call is to be made, the person using thisspecial token will push the slider 43 all the way home thus moving thearm 40 toward the right and closing the contacts 44 and thus completinga normal open connection between the tip of the line 39 and the armatureof relay 26. When the central omce operator responds, the pressure onthe slider 43 may be relieved whereupon the spring 4| will move theslider back a small amount and open the circuit through contacts 44,since this calling connection is not needed after the operator answers.

What is claimed is:

1. In a check-controlled signaling system, a check having a changeableinternal resistance, a circuit into which said check may be inserted,means responsive to the insertion of said check in said circuit forcausing a change in the internal resistance of said check, and meansresponsive to'the sequential values of the resistance of said check fortransmitting a signal.

2. In a signaling system, a normally open circuit including a source ofbattery and a pair of marginal relays in series, one of said relaysbeing responsive to a current of lesser strength than the other, bothsaid relays being responsive to a closure of said circuit through a.path of substantially zero resistance, a coin slot for holding acoin-shaped check, means responsive to the operation of said coin slotfor inserting a coin or a coin-shaped check into the circuit of saidrelays, a special coin-shaped check having a plurality of electricalpaths therethrough each having an appreciable resistance, said specialcoin-shaped check when introduced into the circuit of said relaysconstituting a current-limiting network for operating one only of saidrelays, and signaling means responsive jointly to said relays only whena particular one of said relays operates.

3. In a check controlled signaling system, a portable check having achangeable internal resistance, a circuit into which said check may beinserted, a battery responsive to the insertion of said check in saidcircuit for causing a change in the internal resistance of said check, afirst relay unresponsive to the unchanged resistance of said check andresponsive to the changed resistance thereof, a second relay likewiseunresponsive to the unchanged resistance of said check and responsive tothe changed resistance thereof, each or said relays when operated havinmeans for rendering the other of said relays inoperative, and meanscontrolled by said relays responsive to the sequential values of theresistance of said check for transmitting a signal.

OSCAR A. SHANN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 673,519 Foster May 7, 19011,900,095 Brownstein Mar. 7, 1933 2,332,448 Inglis Oct. 19, 19432,347,777 Hanson .i May 2, 1944

